Communication relay systems for relaying communications performed between communication terminals according to a plurality of communication protocols have been known. As an example of this kind of communication relay systems, a communication relay system disclosed in “Proposal of Pseudonym Provisioning Management Function” by Takao Takenouchi and four others, Proceedings of the IEICE General Conference 2008 (Non-Patent Document 1) includes a pseudonymous identification information acquiring unit and a communication relay unit.
The pseudonymous identification information acquiring unit acquires, for each of the communication protocols, pseudonymous identification information which is different from source terminal identification information included in communication information transmitted in accordance with each communication protocol and used for identifying a communication terminal serving as the source of the communication information, while associating the pseudonymous identification information with the source terminal identification information.
The communication relay unit is adapted such that for each of the communication protocols, when receiving communication information according to each of the communication protocols from a source terminal among a plurality of communication terminals, the communication relay unit replaces the source terminal identification information included in the received communication information with pseudonymous identification information acquired in association with the source terminal identification information. Further, the communication relay unit transmits the communication information after the replacement to a destination terminal among the communication terminals.
According to this communication relay system, it is possible to prevent information for identifying the source terminal which transmitted the communication information from being included in the communication information received by the destination terminal. In other words, communication information can be transmitted from the source terminal to the destination terminal while preventing the source terminal from being identified.    [Non-Patent Document 1] Takao Takenouchi and four others, “Proposal of Pseudonym Provisioning Management Function”, Proceedings of the IEICE General Conference 2008, the Institute of Electronics, information and Communication Engineers, March 2008, B-7-38
However, in the above-described communication relay system, if a new communication protocol is added, it is necessary to alter the pseudonymous identification information acquiring unit. This means that the communication relay system involves a problem of low scalability with respect to addition of communication protocols.
Further, in the communication relay system, maintenance of a unit for acquiring pseudonymous identification information cannot be performed independently for each of the communication protocols. This means that the communication relay system also involves a problem that maintenance of the unit for acquiring pseudonymous identification information cannot be performed easily.